The use of alkylenebis(phosphine oxides) to provide flame-retardance to thermoplastic polymers is known, see U.S. Pat. No. 3,284,543, as is the use of cyano-substituted arylenepoly(phosphine oxides), see U.S. Pat. No. 3,895,048. The alkylene compounds are, however, effective only at relatively high concentrations, e.g., 20-25% for most polymers. Additionally, the carboxyalkyl and carbamoylalkyl derivatives of the alkylene compounds are relatively incompatible with non-polar polymers, such as polypropylene, as are many other of said alkylene compounds, at concentrations ranging upward from about 10%, by weight. As a result, most of the alkylene compounds are extremely difficult to incorporate into said non-polar polymers by conventional extrusion and injection molding techniques since they tend to exude from or form a two-phase system in the polymer. Consequently, uniform dispersions of the flame-retardant additives in the polymers are difficult to obtain.
Another disadvantage, sometimes more serious, is the relatively high water-solubility of the alkylene compounds which, in certain applications, such as in dishwasher and clotheswasher components, tends to cause the compounds to be more readily extracted from the polymer. As a result, the polymers then become more flammable and ultimately fail to pass the Underwriter's Laboratory Test of acceptable flame-retardance.
The need for additional compounds which will function in an acceptable flame-retarding manner in non-polar polymers is therefore readily apparent.